Worm Breeder's Gazette 8(3): 27

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Genetic Lesions Induced by Heavy Ions

G. Nelson, R. Hammen and M. Dyer

I've just begun to do some radiobiology using heavy ions from the 
Berkeley Bevalac accelerator as a way of modeling cosmic rays.  NASA 
is interested in some biological dosimetry for heavy particles such as 
are encountered in earth orbit on the shuttle.  Because of their true 
track structure, measurements in units such as rads and roentgens have 
dubious utility.  Below are some preliminary results from iron 
irradiation experiments which looked for twitchers using Don Moerman 
and Dave Baillie's nicotine trick and some lethals using Raja 
Rosenbluth's eT1 balancer technique.  The particles are highly 
mutagenic and I hope to eventually describe the types and extents of 
lesions caused by single particle interactions.  
An experiment using the BEVALAC accelerator at Lawrence Berkeley 
Laboratory was carried out on June 17, 1984.  The purpose of this 
experiment was to familiarize us with the operation of the facility 
and to demonstrate the proof of concept that mutations could be 
induced in C.  elegans using energetic heavy ions from the accelerator.
Several tests were carried out but two are especially relevant here: 
1) the induction of 'twitcher' mutants in gene unc-22 and, 2) the 
induction of lethal mutations in cross-over suppressed regions of 
chromosomes III and V using a reciprocal translocation strain.  We 
were able to isolate 4 unc-22 mutants from 1965 N2 worms with gonads 
containing nominally 4, 10 and 30 cells with equivalent radiation 
doses of 30.02, 3.24 and 228.9 rads respectively.  Several instances 
of male 'jackpots' were also noted.  (A male 'jackpot' is the 
appearance of large groups of F1 males in broods of virgin 
hermaphrodites presumably due to induced X-chromosome loss; typical 
jackpots were 7 to 17 males per plate of 10 PO's whereas 0, 1 or 2 is 
normal).  6 lethal mutations and one long mutation were isolated from 
96 adult worms tripley heterozygous for dpy-18 III, unc-46 V and the 
reciprocal translocation eT1(III;V) using an equivalent radiation dose 
of 3D.n2 rads.  The type of radiation used was a beam of completely 
ionized iron particles having an energy of 445 MeV per nucleon or a 
total of 24.85 GeV per particle.  The linear energy transfer of these 
particles was determined to be 198 KeV/micron and particles were 
delivered in pulses such that total fluence varied from about 10+E5 to 
10+E7 particle tracks per cm2.  Radiation characteristics were 
determined by Dr.  E.V.  Benton using CR-39 plastic radiation detector 
foils.  We concluded that heavy ions are highly mutagenic in C.  
elegans and that the assays proposed in this proposal are capable of 
detecting genetic lesions induced by them.  Work is in progress to 
determine the locations and nature of the new mutations.  Confirming 
studies using alpha particles from Polonium - 210 also demonstrated 
the effectiveness of high LET particles.  Mutations in unc-22 as well 
as several 'dumpy' and 'cell lineage defective' genes were induced 
with alpha particles using 1st stage larvae or dauer larvae as targets.
The accompanying figure summarizes the BEVALAC results.
[No accompanying